Abstract
Coffee berries are known to release several volatile organic compounds, among which is the spiroacetal, conophthorin, an attractant for the coffee berry borer Hypothenemus hampei. Elucidating the effects of other spiroacetals released by coffee berries is critical to understanding their chemo-ecological roles in the host discrimination and colonization process of the coffee berry borer, and also for their potential use in the management of this pest. Here, we show that the coffee berry spiroacetals frontalin and 1,6-dioxaspiro [4.5] decane (referred thereafter as brocain), are also used as semiochemicals by the coffee berry borer for host colonization. Bioassays and chemical analyses showed that crowding coffee berry borers from 2 to 6 females per berry, reduced borer fecundity, which appeared to correlate with a decrease in the emission rates of conophthorin and frontalin over time. In contrast, the level of brocain did not vary significantly between borer- uninfested and infested berries. Brocain was attractive at lower doses, but repellent at higher doses while frontalin alone or in a blend was critical for avoidance. Field assays with a commercial attractant comprising a mixture of ethanol and methanol (1∶1), combined with frontalin, confirmed the repellent effect of this compound by disrupting capture rates of H. hampei females by 77% in a coffee plantation. Overall, our results suggest that the levels of frontalin and conophthorin released by coffee berries determine the host colonization behaviour of H. hampei, possibly through a ‘push-pull’ system, whereby frontalin acts as the ‘push’ (repellent) and conophthorin acting as the ‘pull’ (attractant). Furthermore, our results reveal the potential use of frontalin as a repellent for management of this coffee pest.
Highlights
The coffee berry borer (Hypothenemus hampei) [Scolytinae: Coleoptera] is the most important and damaging pest of commercial coffee [1], causing losses greater than US$ 500 million annually, and threatening the livelihoods of 100 million small-holder farmers worldwide
The berries infested by 2 initial H. hampei females released the highest amount of (5S, 7S)conophthorin while those infested by 6 colonizing females released the lowest amount
Results from our behavioural assays show that (5S,7S)conophthorin, frontalin and brocain appear to play an important role in the host discrimination and colonization processes of H. hampei
Summary
The coffee berry borer (Hypothenemus hampei) [Scolytinae: Coleoptera] is the most important and damaging pest of commercial coffee [1], causing losses greater than US$ 500 million annually, and threatening the livelihoods of 100 million small-holder farmers worldwide. In previous behavioural studies, while females were attracted to healthy ripe coffee berries, borer-infested berries repelled them [6]. Colonizing females were found to hardly share a host [1,7] These observations suggest the involvement of a female host marking pheromone (HMP) or berry-induced defensive/repellent compounds affecting conspecifics. In scolytinae species, this characteristic behaviour is commonly referred to as ‘maximum attack density’ (MAD), and it involves attack on a unit area of a host in a uniform pattern to enhance spacing for reproduction by individual pest during the host colonization process [8,9,10]. It is desirable to explore whether a similar interaction occurs between the coffee berry borer and its coffee berry host
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